Experimental and numerical study on chloride transport in cement mortar during drying process

Abstract

The evaporation of water from chloride-contaminated concrete during drying process causes reverse convection of chloride ions, resulting in chloride ions to accumulate on the concrete surface, thus affecting concrete durability and service life. In this contribution, the pre-dried treatment, capillary absorption test, free diffusion test, drying test were carried out to experimentally investigate the influence of diffusion and convection on chloride transport. RCM test, isothermal adsorption and desorption test and constant permeability test were used to determine the simulation parameters, thus allowing an accurate simulation of the experiment results. Chloride transport was dominated by the inward diffusion in the free diffusion test, whereas chloride migration in the drying test was affected by the coupling effect of inward diffusion and outward convection. The shorter test days led to a more prominent effect of the reverse convection. The chloride diffusion coefficients varied with the pre-dried days, water-to-cement-ratio and diffusion test type with the best chloride resistance coming from specimens with lower water-to-cement-ratio and shorter pre-dried days. The numerical results agreed fairly well with experimental results obtained from the capillary absorption test, diffusion test and drying test.